Function polylineCenter

libs/leaflet/leaflet-src.js:6541–6597

(latlngs, crs)

   * Returns the center ([centroid](http://en.wikipedia.org/wiki/Centroid)) of the passed LatLngs (first ring) from a polyline.
   */
  function polylineCenter(latlngs, crs) {
  	var i, halfDist, segDist, dist, p1, p2, ratio, center;

  	if (!latlngs || latlngs.length === 0) {
  		throw new Error('latlngs not passed');
  	}

  	if (!isFlat(latlngs)) {
  		console.warn('latlngs are not flat! Only the first ring will be used');
  		latlngs = latlngs[0];
  	}

  	var centroidLatLng = toLatLng([0, 0]);

  	var bounds = toLatLngBounds(latlngs);
  	var areaBounds = bounds.getNorthWest().distanceTo(bounds.getSouthWest()) * bounds.getNorthEast().distanceTo(bounds.getNorthWest());
  	// tests showed that below 1700 rounding errors are happening
  	if (areaBounds < 1700) {
  		// getting a inexact center, to move the latlngs near to [0, 0] to prevent rounding errors
  		centroidLatLng = centroid(latlngs);
  	}

  	var len = latlngs.length;
  	var points = [];
  	for (i = 0; i < len; i++) {
  		var latlng = toLatLng(latlngs[i]);
  		points.push(crs.project(toLatLng([latlng.lat - centroidLatLng.lat, latlng.lng - centroidLatLng.lng])));
  	}

  	for (i = 0, halfDist = 0; i < len - 1; i++) {
  		halfDist += points[i].distanceTo(points[i + 1]) / 2;
  	}

  	// The line is so small in the current view that all points are on the same pixel.
  	if (halfDist === 0) {
  		center = points[0];
  	} else {
  		for (i = 0, dist = 0; i < len - 1; i++) {
  			p1 = points[i];
  			p2 = points[i + 1];
  			segDist = p1.distanceTo(p2);
  			dist += segDist;

  			if (dist > halfDist) {
  				ratio = (dist - halfDist) / segDist;
  				center = [
  					p2.x - ratio * (p2.x - p1.x),
  					p2.y - ratio * (p2.y - p1.y)
  				];
  				break;
  			}
  		}
  	}

  	var latlngCenter = crs.unproject(toPoint(center));
  	return toLatLng([latlngCenter.lat + centroidLatLng.lat, latlngCenter.lng + centroidLatLng.lng]);
  }